1. Field of the Invention
This invention relates to a method for cooling a heating grade heat exchanger in an unsteady state and a method for preventing the fluids under treatment in the heat exchanger from polymerizing.
2. Description of Related Arts
Most heat exchangers are utilized with a specific intention of coolers, heaters, etc. for specified substances. No heat exchanger is designed to fulfill a dual-purpose use for heating and cooling operations in itself. Most heat exchangers are intended to be used most efficiently in specific ranges and are rarely used for any other entirely different purpose in an actual plant.
In a plant engaged in producing such an easily polymerizing compound as (meth)acrylic acid or a (meth)acrylic ester, for example, a power failure compels transferring means such as pumps and stirring and mixing means to discontinue their functions and brings the plant to a stop, with the result that the raw material and the reaction product will stagnate in a vessel and pipes used in the plant and the substances so stagnating will polymerize in the cause of the thermal inertia. Also when the plant incurs difficulty in controlling temperature and pressure on account of an accident or an incorrect manipulation in the equipment or of an abnormal performance of the equipment or an abnormal reaction, the consequent failure to effect temperature control by heat exchange or pressure control by degassing entails either a rise in temperature to the extent of polymerizing the raw material and the reaction product in the vessel and the pipes or a rise in inner pressure of the vessel to the extent of inflicting breakage on the vessel and the pipes and possibly giving rise to an explosive combustible material. It is, therefore, a common practice to lay down a manual for emergency measures and provide a mechanism for coping with an emergency in preparation for the occurrence of such an unsteady state.
To prepare the plant for the emergency, a varying mechanism is adopted for enabling solenoid valves and power valves to be switched manually during the life of the unsteady state, for enabling a feed valve for polymerization inhibitor to be manually switched and consequently permitting the inhibitor to be admitted into the reactor and preventing the contents of the vessel from polymerizing, or for enabling the reactor to be forced cooled down with a blower using a compressed gas or an emergency power source or spontaneously cooled down. The mechanism is aimed at protecting the vessel and the pipes against sustaining a fracture and consequently inflicting a serious damage to the plant owing to the polymerization of the raw material and the reaction product in the vessel and the pipes and the rise of the internal pressure of the vessel. An alternative mechanism may be occasionally adopted for effecting forced discharge of the contents of the reactor and the relevant columns from their interiors by means of a pump using an emergency power source or for effecting gravitational discharge of the contents downward from the reactor and the relevant columns through the lower parts thereof by construction of an underground tank.
The direct engagement of an operator in manually manipulating a valve in the proximity of the reactor or in introducing the polymerization inhibitor into the reactor not only entails danger in itself but also exposes the operator to the possibility of inducing a secondary disaster through a personal negligence possibly committed on account of the urge for promptness of work. The operator also has the possibility of failing to take a prompt measure, of taking only a delayed measure in case of an emergency, or of causing a disaster due to a personal negligence. Particularly in the plant for an easily polymerizing compound, the resumption of the operation thereof after the stop possibly takes up a long time because the contents of the reactor are suffered to polymerize in the cause of the thermal inertia. Further, even the forced cooling by the use of a compressed gas or an air blower entails such problems as suffering generation of a polymer, degrading the plant in productivity, and heightening the cost of production because the cooling operation proceeds with poor efficiency and consumes a long time.
Particularly when the fluid being treated for the production in the plant is an easily polymerizing compound, the process for this production is generally furnished with a means for adding to the fluid a polymerization inhibitor for the purpose of precluding the occurrence of polymerization in the unsteady state. The polymerization inhibitor, when added in an unduly large amount, degrades the plant in efficiency of production by entailing such problems as increasing the viscosity of the fluid during the formation of a finished product through redistillation or changing the state such as deposition.
The present inventor, after pursuing a diligent study repeatedly with a view to fulfilling the object mentioned above has perfected this invention. This invention is aimed at, in a heat exchanger having admitted a heating medium for heating the fluids to be handled therein while the plant is in a steady state, a method for using such devices as are capable of safely and infallibly operating while the plant is in an unsteady state lest they should suffer the raw material and the reaction product to polymerize in the reactor and the relevant pipes, give rise to an explosive combustible material, and suffer the internal pressure of the reactor to rise to the extent of fracturing the vessel and the pipes and consequently inflicting a serious damage on the equipment for production.
Specifically, the object mentioned above is accomplished by the following items (1)-(3).
(1) A method for using a heat exchanger having admitted a heating medium for the purpose of heating a fluid to be handled, characterized by introducing a cooling medium in the heat exchanger in the place of the heating medium during an unsteady state.
(2) A method for preventing an easily polymerizing compound from forming a polymer in a heating grade heat exchanger installed in an apparatus for handling the easily polymerizing compound, characterized by introducing a cooling medium into the heat exchanger in the place of a heating medium during an unstable state.
(3) A method for cooling a fluid to be handled in a heat exchanger having admitted a heating medium for the purpose of heating the fluid, characterized by introducing a cooling medium into the heat exchanger in the place of said heating medium during an unstable state.
These methods are capable of bringing the following effects.
(1) The method allows the number of devices and the installation area thereof to be decreased because the devices used in common with the existing apparatus operating in a steady state and the fluids being handled therein can be cooled. The devices can be quickly and infallibly manipulated without any mistake because their operations are attained simply by switching valves with a low power consumption.
(2) The method, during the course of an unsteady state, is effective in either preventing the contents including the reaction product in the system of the apparatus and the reactor from inducing such an abnormal reaction as polymerization or stopping the abnormal reaction, if induced at all, because the devices can be operated from safe places. Further, the devices can be safely and infallibly operated without suffering the raw material and the reaction product to succumb to polymerization in the vessels and the pipes or causing the internal pressure of the vessels to rise possibly to the extent of fracturing the vessels or the pipes and inflicting serious damage on the apparatus for production.
(3) In the process for the production of an easily polymerizing compound, the method is particularly effective during the course of an unsteady state induced by an abnormality in the columns and the esterification reactor because the possible reaction of polymerization of the easily polymerizing compound can be quickly stopped or abated by introducing into the heat exchanger a cooling medium in the place of a heating medium and consequently cooling the fluids being treated therein. The method, when used in combination with an operation of discharging the fluids, i.e. easily polymerizing compounds, by means of a pump.